This invention relates to surgical fasteners (e.g., staples), and more particularly to a fastener comprising a fastener member and a retainer member and exhibiting improved hemostasis.
Surgical fastening devices allow a surgeon to fasten body tissue by applying surgical fasteners. The fasteners may be applied singly in succession or a number may be applied simultaneously. Surgical fasteners are often made of metals such as tantalum and stainless steel, which are inert. Fasteners of magnesium, which fasteners are gradually absorbed by the body, are also known.
Non-metallic fasteners are also known and may be preferable to metal fasteners in some procedures. For example, non-metallic fasteners can be made X-ray transparent so that they do not scatter X-rays and therefore do not degrade the quality of radiographs as may happen when metal fasteners are used.
On the other hand, objects of non-metallic resinous materials are usually too resilient (i.e., elastic) to hold deformed shapes (assuming plastic flow does not occur). (As used herein, the term "resinous materials" means non-metallic materials, such as natural or synthetic polymers and resins, including protein-based materials, which are relatively flexible and elastic, and which may or may not be absorbable in the body.) The greater elasticity of resinous materials generally makes it impossible to directly substitute such materials for the metal in conventional surgical fasteners.
To overcome this problem, resinous surgical fasteners may be made of two parts: a fastener member and a retainer member. The legs or prongs of the fastener member are driven through one side of the tissue to be fastened and the retainer member interlocks with the prongs of the fastener member on the other side of the tissue to hold the entire fastener structure in place. One such fastener structure and apparatus for applying it are disclosed in Green U.S. Pat. No. 4,402,445, issued Sept. 6, 1983, which is hereby incorporated by reference in its entirety.
A frequent goal in fastening tissue is achieving hemostasis along the fastener line. Hemostasis is achieved by exerting pressure on the tissue from both sides. If metal staples are used, that pressure (hereinafter referred to as "hemostatic pressure") is exerted by and between the base of the staple on one side of the tissue and the crimped legs on the other side of the tissue. In typical crimped metal staples no part of the staple extends beyond the ends of the base. Therefore, a second staple can be applied very close to the first staple, so that the bases of the two staples are in a line. In that case the gap between staples can be quite small so that hemostatic pressure is applied uniformly along the entire staple line.
In contrast, when two-part resinous fasteners are used, hemostatic pressure is exerted by and between the retainer member and the base of the fastener member. In known two-part resinous fasteners the prongs of the fastener member extend from the ends of the base. The retainer member is typically longer than the distance between the prongs and therefore must extend beyond the fastener member base. Accordingly, the bases of adjacent fastener members lying in a line are separated by at least the sum of the distances by which adjacent retainer members extend beyond the associated fastener member bases. Thus, there are gaps between adjacent fastener members. Full hemostatic pressure is not exerted on the tissue in these gaps.
One way to make up for the above-mentioned gaps in a line of resinous fasteners is to apply the fasteners in two parallel rows, with a linear offset between the rows so that the gaps in one row are opposite the bases of the fastener members of the other row. However, this doubles the number of fasteners that are required and increases the area of tissue affected by the fasteners.
Another typical characteristic of resinous materials is that they are not as strong as metals. Surgical fasteners of resinous materials may therefore tend to deform during application to tissue. In particular, the fastener member prongs may tend to splay or spread apart as the prongs are forced through the tissue. One way to overcome this tendency is to provide a metal guide pin adjacent each prong to help the prong penetrate the tissue without deformation. After the fasteners have been applied, the guide pins are withdrawn from the tissue. This guide pin structure has the disadvantage that it increases the complexity and cost of the apparatus for applying the fasteners.